The invention relates to displays, and more particularly to flat panel displays, and most particularly to backlighting for such flat panel displays.
Liquid crystal displays (LCD's) are widely used in applications where space is a limiting factor. One such application that is becoming increasingly common is aircraft cockpit displays for avionics equipment. The principle of operation of LCD's is well known in the art; but for purposes of understanding the background of the present invention, it can be stated that LCD's operate by reducing the transmissibility of light through a thin layer of a liquid crystalline material when an electric field is applied. Since the effect is localized, shapes and characters can be drawn on an LCD by carefully controlling the application of the electric field. Unlike cathode ray tubes which LCD's are replacing, LCD's are not self-illuminating. This does not normally affect daylight use, but under night or other low light level conditions some sort of backlighting is required in order for LCD's to be viewed. Very high brightness ambients also require additional backlight brightness to maintain readability.
Backlighting is conventionally accomplished by locating an electroluminescent device in a sealed cavity directly behind the LCD. The cavity must normally be sealed because LCD's are subject to environmental degradation if exposed to humidity. However, it has been found for some applications that electroluminescent devices do not provide sufficient light. Incandescent lamps could be used, but such lamps are prone to failure and must be replaced. Since LCD's are sealed, incandescent lamps located in the sealed cavity behind the LCD would not be easily accessible. Displays of various kinds have been lighted from the sides, but the light rays from such sources are not equally distributed, leading to bright spots on the edges of the display and dark areas in the center.
It is therefore an object of the present invention to provide a backlighted flat panel display for an electronics device which uniformly distributes the light across the display and eliminates bright and dark spots.
It is another object of the present invention to provide a backlighted flat panel display for an electronics device whose light sources may be replaced without opening the sealed displays.
It is a further object of the present invention to provide a backlighted flat panel display for an electronics device whose light sources may be replaced without removing the electronics from its mounting.
Still other objects will become apparent to the following summary and description of a preferred embodiment of the invention.